📋 Case Study
Iron Ore Mine Waste Rock Long-Term Stability at Brockman 4 (Pilbara)
Massive hematite-goethite waste rock (low sulfide but high Mn/Al) showing delayed acidity and Al leaching post-construction
🏗️ Project Overview
Brockman 4 mine expansion (Rio Tinto, WA), 2018–2023
🎯 Challenge
Massive hematite-goethite waste rock (low sulfide but high Mn/Al) showing delayed acidity and Al leaching post-construction
🔧 Design Approach
Multi-phase reactive transport modeling (CrunchFlow) incorporating Mn redox cycling and Al-hydroxide precipitation kinetics; validated against 5-year field lysimeter data
📐 Design Diagram
AI-generated project design illustration
📐 Key Calculations
Al Solubility Limit
[Al³⁺] = Ksp / [OH⁻]³
Result: 0.18 mg/L
Explained observed Al breakthrough at pH 4.7–5.1
MnO₂ Reduction Rate
k·[MnO₂]·[Fe²⁺]
Result: 1.2×10⁻⁴ s⁻¹
Controlled acid generation lag phase
📊 Results
Model predicted Al peak at year 6.2 ± 0.4 — measured at year 6.5; pH rebounded to 6.1 by year 8; no regulatory exceedances💡 Lessons Learned
- •Goethite reactivity dominates long-term behavior more than hematite
- •Field lysimeters captured heterogeneity missed in lab columns
- •CrunchFlow’s kinetic mineral database required custom Mn-oxide parameters
- •Al leaching preceded acidity — early warning indicator
- •Rainfall intensity distribution (not just total) governed solute transport timing
- •Calibration required 3 independent tracer datasets (Cl⁻, SO₄²⁻, Al)
✅ Key Takeaways
- 1Goethite reactivity dominates long-term behavior more than hematite
- 2Field lysimeters captured heterogeneity missed in lab columns
- 3CrunchFlow’s kinetic mineral database required custom Mn-oxide parameters
- 4Al leaching preceded acidity — early warning indicator
- 5Rainfall intensity distribution (not just total) governed solute transport timing
- 6Calibration required 3 independent tracer datasets (Cl⁻, SO₄²⁻, Al)